The Microsoft Windows Insider Program allows interested Windows fans, enthusiasts, professionals, developers and even Enterprise users to test the upcoming features and updates of Windows 10 before they are released.
This allows Microsoft to get feedback about bugs, UI issues, problems with new features, and compatibility issues in order to fix them before the preview version is released to everyone as a production release.
The Windows Insider Program is optional, but any user with an existing licensed Windows 10 PC can join and start testing out the latest features being developed by Microsoft.
Who should join the program

The Windows 10 Insider Program is not for everyone.
If you want to get access to the upcoming Windows 10 cumulative updates and improvements before the rest of consumers, want to test new features that could be removed before the public release, are ok with installing new Windows 10 versions fairly often, and can deal with bugs, then the Insider Program is for you.
On the other hand, if you are looking for a less buggy operating system (some may debate this) to use in a production environment, you should stick to the current release of Windows 10 and not upgrade to a Windows 10 Insider build.
The good news is that if you join the Windows 10 Insider Program and then decide you no longer want to be part of it, you can leave the program and reinstall Windows 10 using the Media Creation Tool.
How the Windows Insider Program works

To get started with the Windows 10 Insider Program, you need to have a PC running a licensed Windows 10 operating system that will ne switched to Windows 10 Insider builds.
When joining the program, you will first need to select a Ring, or channel, that will tell the Insider Program how often you wish to receive new builds.
Windows 10 Insider Program Rings
When selecting a Ring to join,*you can select one of the following:
Release Preview Ring

Release Preview Ring gives Insiders early access to Windows 10 cumulative updates, app updates, and even drivers for the current production version of Windows that is released.*
The Release Preview Ring will still give you access to new Windows 10 feature updates when the update is stable enough. Furthermore, if you plan on leaving the Insider Program, this Ring is the easiest one to do so as you are still on the production version of Windows 10
Slow Ring

The Slow Ring is your first chance of getting new builds from the development branch of Windows 10 that is not currently released. This Ring, though, delivers new builds at a slower pace so that you are using a more stable operating environment.
It is important to remember that joining Slow Ring will upgrade Windows 10 to the development branch and could still introduce bugs and other issues.
Fast Ring

The Fast Ring is for those who want to be on the cutting edge of Windows development. Users of this build will be among the first to try and test new builds of the upcoming Windows 10 feature update.
As more preview builds are shipped to testers in the Fast Ring, sometimes as fast as once a week, users will be able to test new Windows features as they are added to the operating system and provide feedback directly to the Microsoft developers in some cases.
Users in the Fast Ring should be prepared for critical issues including bugs that may cause Blue screen of Death, break key features or require*significant workarounds. Microsoft validates a preview builds for Fast Ring Insiders on a smaller set of devices, which means some features are likely to fail in some configurations.
There used to a fourth ring called the Skip Ahead ring that allowed Insiders to test even newer Windows 10 builds, but Microsoft has decided to get rid of it.
Once you join a ring, users can perform a "Check for updates" and Windows 10 will show any available preview builds that are available to install. Depending on your ring, this could be new cumulative updates for the current production version (Release Preview Ring) or new Windows 10 Insider builds (Slow and Fast Rings)
Windows 10 Insider build available
How to join the Windows 10 Insider program

Now that you understand how the Windows 10 Insider program works, if you want to join the Windows Insider Program you can perform the following steps:

  1. Make sure you are using a licensed Windows 10 PC and have an existing Microsoft account that you will use to join the Insider program.
  2. Open*Settings.
  3. Navigate to Update & security*and then select the*Windows Insider program settings.
  4. Click the*Get started*button to begin joing the Windows 10 Insider Program. Join the Windows Insider Program
  5. Register your Microsoft account with the Windows Insider Program as shown below. Link Microsoft Account
  6. After your account is linked, you will be prompted to select a Ring, as described in the previous section, that you would like to join. Select Windows Insider Ring
  7. Restart Windows when prompted.

Once you have restarted Windows, you can perform a check for new Windows updates and if any new Insider builds or updates are available you will now be prompted to install them.
Leaving*the Windows Insider program

If you want to exit the Windows Insider program, you have two options;*reinstall the latest Windows 10 production build using the Media Creation Tool or wait until the current development/preview branch is promoted to the production build and stop getting new builds.
The easiest and Microsoft suggested method of leaving the Windows 10 Insider program is to wait for the builds released in the Insider program to be the same as what is offered to everyone in the normal production release. Once this occurs, you can enable an option to stop getting new preview builds and and thus will only receive production updates.
To stop getting new Windows 10 Insider preview builds, you can follow these steps.

  1. Open*Settings.
  2. Navigate to Update & security*and then select the*Windows Insider program settings.
  3. At this screen, you should now enable "Stop getting preview builds" as shown below. Stop getting Insider builds
  4. Select “Stop Insider Preview Builds”
  5. Restart Windows when prompted.

If you wish to go back to production builds before the next version is ready, you will need to use the Media Creation Tool or download the ISO images and reinstall Windows 10 on the PC.